Five hundred draws are made at random with replacement from a box of numbered tickets; 276 are positive. Someone tells you that 50% of the tickets in the box show positive numbers. Do you believe it? Answer yes or no, and explain. 50% positive 50% negative n=500 E(pos) = 250 (267/500) = 55,2% => 5,2% SE = sqrt(0.25)/sqrt(500) = 0.5 * 1/sqrt(500) = 2.24% z = 5.2%/2.24% = 2.33 p = P[2.33] = 0.9901 < 1% -> significant